CN112305525A - Underwater acoustic ranging signal processing method based on spread spectrum technology - Google Patents

Abstract

The invention provides an underwater acoustic ranging signal processing method based on a spread spectrum technology. After data received by the hydrophone is subjected to signal conditioning processes such as amplification and filtering, original data is formed through digital acquisition, and then signal processing processes such as quadrature baseband demodulation, low-pass filtering and down-sampling are carried out on the original data to form primary processing data. And after generating original reference data according to the spread spectrum parameters of the known underwater acoustic signals, carrying out orthogonal baseband demodulation, low-pass filtering, down-sampling and conjugation processing to form preliminary reference data. And performing convolution on the primary processing data and the primary reference data, and then performing modulus extraction to obtain a detection signal. In order to accurately estimate the signal propagation time, the clocks of the signal beacon transmitter and the underwater robot receiver are required to be synchronized, and the signal transmission time is the whole second of the clock. Different beacon transmitters and signal transmission moments are distinguished through different spreading codes of the same code family, so that the ranging service with high updating speed is realized. The underwater acoustic positioning navigation system is mainly used for underwater acoustic positioning navigation service meeting the requirement of simultaneous operation of a plurality of underwater robots.

Description

A Signal Processing Method of Underwater Acoustic Ranging Based on Spread Spectrum Technology

technical field

The invention belongs to the field of underwater positioning and navigation, and in particular relates to a signal processing method for underwater acoustic ranging.

Background technique

Underwater robots can replace humans in deep water to complete the detection and development of marine resources, saving a lot of costs for production. At the same time, it reflects important value in protecting national security and people's property. Underwater positioning and navigation technology is the difficulty and focus of underwater robot technology. In practical applications, due to the small size and light weight of underwater vehicles, which are easily affected by the underwater environment, underwater positioning and navigation has become a more difficult problem. . At present, the navigation systems used in underwater robots are generally divided into two categories according to their working methods: one is an autonomous navigation system that does not require external information, such as an inertial navigation system; the other is a navigation system that relies on external information. Such as GPS/Beidou/Galileo and other satellite radio navigation systems, underwater acoustic positioning and navigation systems, etc. The inertial navigation system needs to complete the navigation with the help of the output of the inertial device. However, due to the drift problem of the inertial device itself, errors will occur, and the positioning error will accumulate over time without correction, so it cannot be used alone in long-range underwater missions. Although the positioning accuracy of satellite radio navigation systems such as GPS is relatively high, electromagnetic waves are easily absorbed when propagating in water and cannot be used in long-range missions. The underwater acoustic positioning and navigation system arranges reference beacons in the working sea area in advance, and measures the distance by measuring the propagation time of the underwater acoustic signal from the transmitter to the receiver, which can make up for the inertial navigation system and the satellite radio system in the long-range mission of the underwater robot. insufficient. However, the shortcomings of the traditional underwater acoustic positioning and navigation system are also very obvious. Due to its question-and-answer mode, the number of underwater robots it can accommodate is limited, and the update rate of the positioning service is too slow. Therefore, it can be considered to study the signal processing algorithm with the help of spread spectrum technology to solve the above problems.

The invention is based on the spread spectrum technology, different beacon transmitters transmit positioning service signals to the outside, and the underwater robot receiver receives the underwater acoustic signals for self-position calculation, avoiding the system accommodation caused by the question-and-answer operation mode of the traditional underwater acoustic positioning system. The problem of limited number of underwater robots. Different transmitters and transmission signal timings are distinguished by different spreading codes of the same code family, so as to realize the ranging service with faster update speed. In order to ensure the realization of the above functions, the clocks of the signal transmitter and the signal receiver need to be synchronized, and the signal transmission time is an entire second of the clock. The invention provides theoretical support and engineering application guarantee for the collaborative operation of underwater robots.

SUMMARY OF THE INVENTION

The present invention relates to an underwater acoustic ranging signal processing method based on spread spectrum technology, comprising the following steps:

A1: After the data received by the hydrophone is subjected to signal conditioning such as amplification and filtering, the original data C1 is formed by digital acquisition through the analog-digital acquisition circuit;

A2: Perform signal processing processes such as quadrature baseband demodulation, low-pass filtering, and downsampling on the original data C1 to form preliminary processed data C2;

A3: According to the existing signal parameters and the generated original reference data C3, perform quadrature baseband demodulation, low-pass filtering, down-sampling and conjugate processing to form preliminary reference data C4;

A4: Perform a convolution operation on the preliminary processed data C2 and the preliminary reference data C4 and take the modulo to obtain a detection signal C5;

A5: Compare the detection signal C5 with the threshold value, and judge the signal propagation time when it is greater than the threshold value, and then obtain the distance between the transmitter and the receiver.

In order to accurately estimate the signal propagation time, it is necessary to ensure that the clocks of the beacon signal transmitter and the underwater robot signal receiver are synchronized.

The signal transmission time is the start of the whole second of the clock, that is, the whole number of seconds, zero milliseconds, zero microseconds, and zero nanoseconds.

Different transmitters and transmission signal moments are distinguished by different spreading codes of the same code family. If the number of transmitters is N, the number of signals transmitted in a whole second is marked as M, and there are D groups of different pseudorandom codes in the same code family, the relationship between the three needs to be satisfied:

N×M≤D

In order to reduce the amount of calculation caused by traversing different spreading codes, it is necessary to minimize the number of times M in a whole second of the transmitted signal. If the maximum working distance of underwater acoustic ranging is L, the speed of sound in water is c, and the update frequency of underwater acoustic positioning service is H seconds, then M needs to satisfy:

为向上取整。in,

to round up.

Compared with the prior art, the beneficial effects of the present invention are:

When positioning and navigation services are required for the collaborative operation of multiple underwater robots, beacon transmitters can be used to transmit signals, and the underwater robots only receive acoustic signals. In this way, the situation that the system accommodates the limited number of underwater robots caused by the question-and-answer mode of the traditional underwater acoustic positioning system is avoided. In addition, the present invention adopts different pseudo-random code signals to mark the start time of transmitting the signal, which makes it possible for the underwater robot to have a higher update rate requirement of the positioning service. The invention provides a theoretical basis and an engineering application method for the cooperative work of multiple underwater robots.

Description of drawings

Figure 1 is a simulation diagram of a signal generated by a signal generator.

Figure 2 is the ranging signal received by the simulated hydrophone.

Figure 3 is a signal simulation diagram after low-pass filtering.

FIG. 4 is a schematic diagram of a detection signal finally obtained after processing.

Detailed ways

The present invention relates to an underwater acoustic ranging signal processing method based on spread spectrum technology, comprising the following steps:

A1: After the data received by the hydrophone is subjected to signal conditioning such as amplification and filtering, the original data C1 is formed by digital acquisition through the analog-digital acquisition circuit;

A2: Perform signal processing processes such as quadrature baseband demodulation, low-pass filtering, and downsampling on the original data C1 to form preliminary processed data C2;

A3: According to the existing signal parameters and the generated original reference data C3, perform quadrature baseband demodulation, low-pass filtering, down-sampling and conjugate processing to form preliminary reference data C4;

A4: Perform a convolution operation on the preliminary processed data C2 and the preliminary reference data C4 and take the modulo to obtain a detection signal C5;

A5: Compare the detection signal C5 with the threshold value, and judge the signal propagation time when it is greater than the threshold value, and then obtain the distance between the transmitter and the receiver.

Further, in order to accurately estimate the signal propagation time, it is necessary to ensure that the clocks of the beacon signal transmitter and the underwater robot signal receiver are synchronized.

Further, the signal transmission time is the start of an entire second of the clock, that is, an integer second, zero milliseconds, zero microseconds, and zero nanoseconds.

Further, different transmitters and transmission signal times are distinguished by different spreading codes of the same code family. If the number of transmitters is N, the number of signals transmitted in a whole second is marked as M, and there are D groups of different pseudorandom codes in the same code family, the relationship between the three needs to be satisfied:

N×M≤D

Further, in order to reduce the amount of calculation caused by traversing different spreading codes, it is necessary to reduce the number M of the whole second of the transmitted signal as much as possible. If the maximum working distance of underwater acoustic ranging is L, the speed of sound in water is c, and the update frequency of underwater acoustic positioning service is H seconds, then M needs to satisfy:

为向上取整。in,

to round up.

The above calculation steps are described in detail in combination with the simulation data.

Assume that the working depth requirement of the system is 6000m;

The signal center frequency is set to 11kHz;

The propagation loss is 86dB;

The noise source level is 85dB;

The sound source level of the transducer is 171dB;

The detection threshold is 20dB;

The spread spectrum code adopts 7-level Gold code, and the code rate is 2.2kHz;

The signal sampling rate is 70kHz;

The demodulation frequency is 8kHz;

The passband of the low-pass filter is 0 to 6 kHz.

The simulation results are shown in Figures 1 to 4. As can be seen from FIG. 4 , when the signal-to-noise ratio of the transmitted signal generated according to FIG. 1 is 0 dB, the signal processing method provided by the present invention can realize the correct processing of the underwater acoustic ranging signal.

Claims (5)

1. An underwater acoustic ranging signal processing method based on spread spectrum technology comprises the following steps:

the method comprises the following steps: after signal conditioning such as amplification and filtering is carried out on data received by a hydrophone, original data are formed through digital acquisition;

step two: performing signal processing processes such as quadrature baseband demodulation, low-pass filtering, down-sampling and the like on the original data to form primary processing data;

step three: and performing quadrature baseband demodulation, low-pass filtering, down-sampling and conjugation processing to form preliminary reference data according to the existing signal parameters and the generated original reference data.

Step four: and performing convolution operation on the preliminary processing data and the preliminary reference data, and then performing modulus extraction to obtain a detection signal.

Step five: and comparing the detection signal with a threshold, judging the signal propagation time when the detection signal is larger than the threshold, and further solving the distance between the beacon transmitter and the underwater robot receiver.

2. The underwater acoustic ranging signal processing method based on the spread spectrum technology as claimed in claim 1, wherein the clock synchronization between the beacon signal transmitter and the underwater robot signal receiver is required to be ensured in order to accurately estimate the signal propagation duration.

3. The underwater acoustic ranging signal processing method based on the spread spectrum technology as claimed in claim 1, wherein the signal transmission time is the beginning of an integer second of the clock, i.e. an integer second is zero millisecond, zero microsecond and zero nanosecond.

4. The method of claim 1, wherein the different transmitters and the time of transmitting signals are distinguished by different spreading codes in the same code family. If the number of the transmitters is N, the number of the transmitters is used for marking the whole second moment of the transmitted signal as M, and the same code family has D groups of different pseudo-random codes in common, the relationship of the three needs to satisfy:

N×M≤D 。

5. an underwater acoustic ranging signal processing method based on spread spectrum technology as claimed in claims 1 and 4, wherein the number of whole second time instants M of the transmitted signal is required to be minimized in order to reduce the amount of calculation caused by traversing different spreading codes. If the maximum acting distance of the underwater acoustic ranging is L, the sound velocity in water is c, and the updating frequency of the underwater acoustic positioning service is H seconds, M needs to satisfy the following conditions:

wherein ,

is rounded up.

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